1. Field of the Invention
The present invention relates to a solid-state imaging device and to a manufacturing method thereof, and in further detail relates to a solid-state imaging device that can form an image by light impinging on a photo diode formed on a substrate surface, and to a manufacturing method thereof.
2. Background Art
Solid-state imaging devices which use a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) are being required to have cost reductions by reducing the chip size and to have increased resolution with increased pixels, and reducing the pixel size is critical.
However, a solid-state imaging device normally consists of a semiconductor substrate and a multilayer wiring layer established thereon. Furthermore, a photoreceptor known as a PD (Photo Diode) is formed on the semiconductor substrate surface, and light coming from the outside passes through a cylindrical light guiding unit established in the multilayer wiring layer and reaches the PD. Therefore, if the pixel size is reduced, the photoreceptor surface area will be smaller and the aspect ratio of the light guiding unit will increase, the amount of incident light for each pixel will be reduced, sensitivity will be reduced, the amount of skewed light entering the peripheral areas of the chip will be dramatically reduced, and sensitivity variation (shading) will be noticeable. Furthermore, the distance between the light guiding units will be shorter so the light from adjacent pixels will easily mix, and crosstalk will easily occur.
The point for resolving these problems is how to increase the light collecting efficiency of the PD. Several methods have been proposed as means for increasing the light collecting efficiency of the PD. For example, a method to increase the efficiency of using the light that impinges on the light guiding unit has been proposed wherein an on-chip micro-lens is established on the multilayer wiring layer along with an inner lens (lens inside the layer) consisting of a highly refractive material such as SiN, and this inner lens is located on the light path between the PD and the on-chip micro-lens. Furthermore, another method has been proposed where a material with a refractive index higher than an interlayer insulative film is embedded in the light guiding unit in a multilayer wiring layer to form a light guiding wave path, and the light that impinges on the light guiding unit is enclosed inside the light guiding wave path in order to transfer the light to the PD with high efficiency. (For example, refer to Patent Documentation 1).
However, with the aforementioned methods, if the pixel size becomes much smaller in the future and the diameter of the light guiding unit become smaller than approximately ½ of the visible light wavelength, impinging light on the light guiding unit will become difficult, and there will be problems in that the increased efficiency of collecting light to the PD will be insufficient.